You can track that if you setup your site with Google Analytics, or even to a lesser extent on Project Wonderful.
Project Wonderful is good for advertising on, you can bid on ad boxes for free or bid a few cents a day. If you find a good similar site to place an ad on on PW then you can get great traction. On a few sites that I bid on, I can reach 200 hits a day with them.
Top Webcomic has been pretty good if you can stay between the top 300 spots on the list.
Livestreaming is the BEST way to engage with readers and have fun with them. I've also received random followers that found me through surfing picarto.
Guest comics, fan art, and doing event/collabs with fellow comic creator does amazing at reaching new readers.
All these methods get a mix of General comic audience and niche. For reaching a more general comic audience I recommend comic conventions, joining comic communities (like #webcomicchat and #comictalk on Twitter), and entering art contests.
So much to do, an artist's job is never done ^_^